The present invention relates to protective sleeves intended to preserve the flexible pipes used to transport fluids such as hydrocarbons and in particular gas, between the offshore installations.
Such pipes are said to be non-linked or linked depending on their structures, which comprise wound superposed layers. Precise definitions of these structures can be found in the “recommended practice for flexible pipe” documents published by the American Petroleum Institute (API).
More particularly, the invention relates to a stiffening sleeve intended to be mounted around a longitudinal portion of flexible pipe, usually close to an end of the pipe, to withstand the deflection of said longitudinal portion according to any bend so as to safeguard it from any irreversible damage. The damage may result either from an excessive deflection of the portion of flexible pipe by a small bending radius or else from the repeated deflections, provoked by the movements of the sea swell or currents.
Stiffening sleeves that are known and widely used in the field of flexible oil pipelines consist of a tapered body molded from a plastic material, usually polyurethane. These stiffening sleeves, or “bend stiffeners” are then fitted around the flexible pipe before the end piece is installed. Their weight is relatively high, several hundred kg, for example 900 kg. Also, handling and installing this type of sleeve is fairly difficult. Furthermore, they are made from a single piece of a polymeric material whose cost is relatively high and which requires an appropriate molding technique. Another drawback is the replacement of this type of stiffening sleeve, which cannot be done without cutting the section of flexible pipe bearing it.
To overcome the drawbacks of the above-mentioned stiffening sleeves, consideration has been given to fitting the portion of pipe through a set of collars, which are distributed at regular intervals over the length of the portion of flexible pipe to be reinforced. These collars include axial drill holes intended to receive flexible metallic rods regularly distributed around the pipe.
The document WO2006/033579 discloses such a stiffening sleeve for flexible pipe transporting hydrocarbons. The elastic properties of the metallic rods and their spacings around the circumference of the portion of flexible pipe define the stiffness of the sleeve and consequently the resistance to deflection undergone by the portion of flexible pipe.
However, when the deflection forces exerted on the portion of pipe are too great, the metallic rods buckle and the stiffening sleeve is ultimately bent beyond a bending radius that is acceptable to the pipe, and it is degraded.
Also, a problem which arises and which the present invention seeks to resolve is to provide a protective sleeve which allows not only the deflection of the flexible pipe to be withstood, but more, it makes it possible to prevent the deflection beyond a limiting bending radius.